Estrogen's influence on GH secretion is significantly responsible for the age and gender differences in GH secretory profiles. We will test the hypothesis that estrogen replacement in postmenopausal women increases growth hormone (GH) secretion by decreasing the ability of GH to negatively regulate its own secretion basally and GH secretion stimulated by growth hormone releasing hormone (GHRH), growth hormone releasing peptide-2 (GHRP-2), and exercise.